1. Field of the Invention
The present invention relates to non-woven fabrics, and more particularly, to bioabsorbable non-woven fabrics for use in medicine and surgery.
2. Description of the Related Art
Non-woven fabrics are porous, textile-like materials, usually in flat sheet form, composed primarily or entirely of fibers assembled in webs. Non-woven fabrics are also known as bonded fabrics, formed fabrics, or engineered fabrics and are manufactured by processes other than spinning, weaving or knitting.
The basic structure of non-woven fabrics is based on arrangements of fibers. Individual fibers are typically arranged more or less randomly. The tensile, stress-strain, and tactile properties of the non-woven fabric ordinarily stem from fiber to fiber friction created by entanglement and reinforcement of yarns, scrims, nettings and/or adhesive or other chemical and physical bonding.
Various methods are known for production of non-woven fabrics and include such procedures as crimping of multifilament yarn, cutting of yarn into staple fibers, carding of staple fibers, air laying, wet forming, spunbonding, spunlacing, needlepunching and stitchbonding. Such procedures are discussed generally in the Encyclopedia of Polymer Science and Engineering, Vol. 10, pp. 204-253 (1987) incorporated herein by reference. These methods and others are used to produce non-woven fabrics from a variety of polymeric materials.
Certain non-woven fabrics have been used in medicine and surgery as all-purpose pads, pledgets, wound dressings, sponges, hemostats and the like. Bioabsorbable polymers such as lactide, glycolide and dioxanone have been incorporated in non-woven fabrics when contact with a wound or implantation into a patient's body is a possibility. In U.S. Pat. No. 3,875,937 polyglycolic acid is described as being fashioned into sterile gauze, felt or velour dressing and used to protect a wound surface or as a bolster to prevent a suture from cutting into tissue. However, no guidance is given relative to any procedures or specifications for forming such a non-woven fabric. U.S. Pat. Nos. 3,937,223 and 4,128,612 describe compacted surgical hemostatic felt and making absorbable felt from polyglycolic acid or a polymer having an ordered configuration of glycolic units and lactic acid units, or poly(N-acetyl-D-glucosamine). The hemostatic felt is described as produced by random formation by air scattering of a felt followed by heat embossing. Heat embossing appears to be a crucial aspect of the hemostatic felt, i.e., heat embossing and compacting fibers on the tissue contacting surface of the hemostat is stressed and said to aid in causing the felt to adhere sufficiently closely to hold the felt to the wound, and compacting the free surfaces reduces the tendency for blood to flow through the felt.
Bioabsorbable pledgets made from non-woven fabrics are described by Nakamura et al. in Thorac. Cardiovasc. Surg. pp. 81-85 (1990) and Medical Textiles For Implantation pp. 329-332 (1990) for use in cardiovascular and pulmonary surgery. The pledgets are said to be used to reinforce suture points and stop leakage from needle holes. However, few details relating to the production of the fabrics are provided. Commercially available resorbable pledgets, i.e., Ethisorb-710 (available in Germany from Ethicon, Inc.) are made of an absorbable composite material consisting of polyglactin and polydioxanone. Fibers of polyglactin and polydioxanone are welded together by means of heat and pressure to form piedgets.
Thus, it is seen that non-woven fabrics may be used in medicine for a variety of purposes. Properties of non-woven fabrics can be varied depending on constituent materials and the manufacturing process. Desirable characteristics of a bioabsorbable non-woven fabric include strength retention as measured by needle pull out, ease of needle penetration (both wet and dry) and low density. Low density is preferable for bioabsorbable implants since, for a given volume of implant, less material needs to be absorbed by the body. As density decreases, however, strength per unit volume typically decreases.
Therefore, the need exists for a reproducible superior low density bioabsorbable non-woven fabric which has requisite strength retention in the body. A need also exists for a low cost and simple method of manufacturing low density bioabsorbable fabrics.